If you subscribe to the mantra go big or go home, do not leave Yellowstone without visiting Midway Geyser Basin. The main attraction on this 0.8-mile boardwalk is Grand Prismatic Spring, the largest hot spring in Yellowstone National Park. The easy loop also passes Excelsior Geyser, a steaming pool of vibrant blue water that isn’t far behind in the contest over surface area. Go see the big hydrothermal features at Midway Geyser Basin before go home.
From the trailhead parking area, take the wooden bridge across the Firehole River toward an unusual landscape. Water streams down the opposing river bank from the hydrothermal pools above, creating colorful channel lined by yellow and orange bacterial mats. After crossing the bridge, you will head up the slope alongside the runoff from Excelsior Geyser, which adds 5,800,000 gallons of nearly boiling water to the river each day. Follow the water to it’s source, a steaming crater containing a vibrant blue pool. Excelsior Geyser did not always look so calm, as a panel along the boardwalk explains:
In the 1800s Excelsior Geyser erupted in bursts 50 to 300 feet high. The thermal violence formed the jagged crater and apparently ruptured the geyser’s underground system, causing eruptions to cease after 1890. On September 14, 1985, Excelsior roared back to life with forty-seven hours of major eruptions. It is impossible to predict when this dormant but powerful geyser’s next eruption will occur. Though its eruptions have been erratic, the geyser’s outflow is nearly constant, pumping more than 4,000 gallons of boiling water per minute over the crater rim into the Firehole River.
You will come to a split in the boardwalk less than a quarter mile from the start. Ahead is a 1/3-mile loop that will take you past Grand Prismatic Spring. You may head left or right. There are no other junctions on the boardwalk, so it is impossible to get lost. Chances are, you will be drawn to the left first, to continue walking around Excelsior Geyser.
Unlike other pools in the park, Excelsior Geyser is lined by short jagged cliffs that hint at a violent past. Another sign along the walkway explains how the unique shape of Excelsior Geyser makes it especially useful to scientists.
Excelsior Geyser’s rugged crater was created by rare massive geyser eruptions. Surprisingly, it also preserves a record of past life. For thousands of years, microbes have grown in the runoff channels extending from nearby Grand Prismatic Spring. These vast communities were buried alive as the flowing hot water deposited a crust of silica minerals. The resulting deposit, called sinter, preserved the shape of the microbial mat it entombed. As new mats grew, more layers developed. Today’s formation is the result of this interplay between its living and nonliving components. Yellowstone’s hydrothermal features provide a glimpse into the distant past when intense volcanism was widespread on the young Earth. The lifeforms found here help scientists understand the type of life that likely arose and diversified billions of years ago on our planet.
The colors found across the hydrothermal features at Midway Geyser Basin are created by thermophiles, microorganisms that love heat. Thermophiles change color depending on the temperature of the water they are in. These extreme organisms live in water once thought to be too hot to support life.
After leaving Excelsior Geyser, the walkway continues up a gently sloping plane toward Grand Prismatic Spring. The slick surface surrounding the boardwalk is covered in rippling water running. Thermophiles color the surface in oranges, reds, and browns.
Do not attempt to touch the water flowing over the bacterial mat and stay on the boardwalk as it nears the edge of Grand Prismatic Spring, Yellowstone’s biggest and possibly most vibrant hot springs. Grand Prismatic Spring is large enough to be a lap pool, about 375 feet across and 125 feet deep, but you would not want to step one toe into the 160-degree (Fahrenheit) water. Steam rises from the vast surface, making it difficult to see across the entire pool all at once. Depending on which way the wind is blowing, the mist can pass right over you as you stand mesmerized on the boardwalk. The white steam rises from a light green and blue pool with a yellow rim, encircled by a red and brown runoff surface. It is a spectacular natural spectrum, illuminated by the millions upon millions of microorganisms that somehow survive in the spring.
A sign along the boardwalk explains how Grand Prismatic Spring functions:
Deep beneath us, magma from an underground active volcano heats water that rises to the surface through fissures in the rocks. The result is a hot spring that pours almost 500 gallons of hot water each minute into the Firehole River. Minerals dissolved in the hot water are deposited and gradually build the gracefully terraced shoulders of this feature.
After leaving Grand Prismatic Spring, the boardwalk circles back toward Excelsior Geyser, passing Opal Pool and Turqoise Pool along the way. While both pools are beautiful, they don’t compete with the other two for magnitude. Complete the loop by turning left at the junction, and walk back past the runoff from Excelsior Geyser and over the bridge to finish the walk.
Yellowstone National Park has an entrance fee, but no permit is required to explore Midway Geyser Basin. Stay on the boardwalk and do not touch any hydrothermal features (or throw anything in).
To get to the trailhead: From Old Faithful, drive 6 miles north on Grand Loop Road (Route 89) and turn left (west) into the parking area for Midway Geyser Basin. From the other directions, drive 10.5 miles south of Madison Junction on Grand Loop Road to reach the trailhead. Midway Geyser Basin is 3.5 miles north of the trailhead for Buscuit Basin and two miles south of the trailhead for Fountain Paint Pot Trail.
Trailhead address: Grand Loop Road (Route 89), Yellowstone National Park, WY 82190
Trailhead coordinates: 44.528424, -110.836253 (44° 31′ 42.32″N 110° 50′ 10.51″W)
You may also view a regional map of surrounding Wyoming trails and campgrounds.
This 2/3 of a mile loop explores hydrothermal features in Upper Geyser Basin like Black Opal Pool, Sapphire Pool, and Black Pearl Geyser.
|Old Faithful Geyser|
The tall, frequent eruptions of Yellowstone’s most famous geyser have been dazzling visitors for over a century and are easy to witness today.
|Fountain Paint Pot|
This half-mile loop in Lower Geyser Basin passes geysers, hot springs, mudpots, and fumaroles – all of the hydrothermal features found in Yellowstone.
|Monument Geyser Basin|
This 2.8-mile hike reaches a rarely visited hydrothermal area that is boardwalk-free and fun to explore.
This 1.1-mile hike circles a hillside hydrothermal area, passing bursting mudpots, bubbling hot springs, and mesmerizing milky blue pools.
|Back Basin of Norris Geyser Basin|
This loop passes Steamboat Spring, the world’s largest geyser, and several other hydrothermal features.
|Porcelain Basin of Norris Geyser Basin|
This pair of loops explores a stark basin with an impressive collection of geysers and hot springs.
|More trails in Yellowstone|
Explore other hikes to waterfalls and hydrothermal hot spots in Yellowstone National Park.
|Yellowstone National Park Campgrounds|
There are 12 developed campgrounds with over 2,000 total sites spread throughout Yellowstone.